M.U.G.E.N's default motif. Many different looks are possible for the engine.

M.U.G.E.N is a freeware 2D fighting game engine designed by Elecbyte, written in C with the Allegro library.

The engine was originally released July 17, 1999. Beta versions of it were made to work on DOS, Linux and Windows platforms, distributed through their website. The engine allows users to insert created characters, background stages, and other game objects through interpreted text files, graphics, and sound compilations to create a functioning fighting game similar to commercial games. While the engine is set up primarily for fighting game development, several other game types have been developed using it, including shooter and platform style games. Officially, Elecbyte claims to have forgotten what the acronym M.U.G.E.N stood for, but the readme documentation states that its meaning referred to the days when the engine was meant to emulate shooting games as opposed to fighting games.

The development of the DOS version ceased when Elecbyte switched to the Linux platform in November 2001. For a time, Elecbyte had posted a request for donations on their site to legally obtain a Windows compiler to make a Windows version of M.U.G.E.N. However, the development group discontinued the project in 2003 and shut down their site. One version for Windows, WinM.U.G.E.N, circulates on the internet. The website resurfaced in 2007 with a FAQ, though it has not been updated since. Only the software itself is part of Elecbyte’s license, so creations such as characters and stages for use with M.U.G.E.N are covered. Elecbyte itself has not made a public statement since 2003, when they stated that the project had “hit a snag”.

An example of M.U.G.E.N's gameplay: original character Dragon Claw faces Darkstalkers character Hsien-Ko on the RAW is WAR arena. The skin used for the game is based on Capcom vs. SNK 2.

The engine allows for seven buttons for gameplay along with the directional keys, in order to accommodate six-button fighters, four-button fighters, or any other variation. The main mode of play is Arcade mode, where a character fights a set number of random characters. It also has a versus mode that features one on one combat and team combat. The survival mode allows for an endless stream of opponents to be fought with one or two characters until the player is defeated.

Elecbyte created a single character, Kung Fu Man, for the engine. He is a practitioner of karate with hair spiked straight up and closed eyes who wears a gi with a black shirt underneath, blue shoes, and a headband. His movelist serves as a guideline for basic coding techniques in the engine.

Although M.U.G.E.N is a 6 button game engine, you can also set button combinations such as F+A to add more attacks to the character.